This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A333817 #7 Apr 06 2020 18:23:28
%S A333817 1,0,0,0,0,1,1,0,0,0,1,0,0,0,0,1,1,1,0,0,1,0,0,0,0,1,1,0,0,0,1,0,1,1,
%T A333817 0,1,1,0,0,0,1,0,0,0,0,1,1,1,0,0,1,0,0,1,1,1,1,0,0,0,1,0,1,0,0,1,1,0,
%U A333817 0,0,1,0,0,1,0,1,1,1,0,1,2,0,0,0,0,1,1,0,0,0,1,0,1
%N A333817 G.f.: Sum_{k>=1} x^(k*(5*k - 3)/2) / (1 - x^(5*k)).
%C A333817 Number of ways to write n as the difference of two heptagonal numbers.
%F A333817 G.f.: Sum_{i>=0} Sum_{j>=i} Product_{k=i..j} x^(5*k + 1).
%t A333817 nmax = 93; CoefficientList[Series[Sum[x^(k (5 k - 3)/2)/(1 - x^(5 k)), {k, 1, nmax}], {x, 0, nmax}], x] // Rest
%Y A333817 Cf. A000566, A001227, A034178, A333815, A333816, A333818.
%K A333817 nonn
%O A333817 1,81
%A A333817 _Ilya Gutkovskiy_, Apr 06 2020